Coach Nate Oats knew the Bulls had a shot at beating big, bad Arizona, but only if they could put lots of pressure on Arizona's guards and make them shoot from the perimeter.

It worked to perfection.

Call them the bracket-busting Bulls.

Pushing the pace and hounding Arizona into submission, 13th-seeded Buffalo pulled off the NCAA Tournament's biggest upset of the opening round, rolling to an 89-68 victory over the fourth-seeded Wildcats in the South Region on Thursday night.

"I felt like we had a shot," Oats said. "I didn't think we were going to win it like that."

The MAC's Bulls have a decided size disadvantage against the Pac-12's Wildcats and their pair of their 7-footers.

Buffalo (27-8) shredded Arizona's defense with its quickness, getting to the lane for shots at the rim and kickouts to shooters.

Defensively, the Bulls pressured Arizona's guards and collapsed around its big men in the lane, forcing the Wildcats (27-8) to the perimeter. Arizona couldn't convert, going 2 for 18 from beyond the arc while the Bulls knocked down 15 of 30.

And, boy, did they run — right into the round of 32 against Kentucky on Saturday.

"With us being a MAC, it's easy to look at us as a team that can't compete with a high-major, a team that has four NBA prospects," Clark said. "We know deep down from looking at the film and getting our confidence right that we could play with those guys. We came and played hard."

Arizona was bewildered by Buffalo's quickness and had a hard time getting the ball into Pac-12 player of the year Deandre Ayton. He still finished with 14 points and 13 rebounds, but the Bulls prevented him from dominating, as he had most of the season.

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Now the Wildcats' tumultuous season is done and so is the Pac-12 — Arizona was the last of the conference's three teams still in the bracket. It's the first time since 1996-97 a school from the six major conferences failed to send a team to the round of 32.

"They overwhelmed us in the second half, on offense and defense," Arizona coach Sean Miller said.

Arizona has played through one of the most difficult seasons in program history. The Wildcats were twice entangled in a federal investigation into nefarious recruiting practices and lost one of their best players twice to injury. Allonzo Trier missed two games after testing positive for the same banned substance that cost him 19 games a year ago.

Outside of an 0-for-3 trip to the Bahamas, their focus on the court rarely wavered. Arizona won the Pac-12 regular-season title and routed Southern California in the tournament title game, becoming the second team in conference history to sweep both in consecutive seasons.

"We endured a lot from the beginning," Arizona point guard Parker Jackson-Cartwright said. "People kind of wrote us off. And I thought we responded every time that happened."

The Wildcats were the No. 4 seed in the South, but Buffalo was not an easy matchup.

Harris and Clark used their quickness to combine for 27 first-half points, and the Wildcats went 1 for 8 from 3-point range to trail Buffalo 40-38.

Buffalo used a similar blueprint to build a 65-55 lead midway through the second half. Massinburg banked in a 3-pointer to stretch the lead to 13 and the Bulls kept building it, racing off to the program's biggest victory.

BIG PICTURE

Arizona will be in rebuilding mode this offseason with Ayton, Trier and Rawle Alkins headed to the NBA and a thin recruiting class so far.

Buffalo picked up the program's biggest win with its best game of the season.

BUSTING OBAMA'S BRACKET

Former President Barack Obama picked Arizona to beat Buffalo in his bracket. He was left disappointed along with millions of others, but the Bulls aren't going to apologize.

"I noticed President Barack Obama picked Arizona to beat us," Massinburg said. "So I just wanted to say, 'President Obama, I'm sorry but I had to.'"

UP NEXT

Buffalo will face Kentucky in the round of 32 on Saturday.

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More AP college basketball: https://collegebasketball.ap.org ; https://twitter.com/AP_Top25 and https://www.podcastone.com/ap-sports-special-events